1. Field of the Invention
The present invention relates generally to a contact for a vacuum interrupter, and particularly to a contact for a vacuum interrupter which has large current interrupting ability and breakdown voltage ability.
2. Description of the Related Art
Vacuum interrupters have low maintenance, no environmental pollution and splendid current interrupting ability. As a result, they find increasing use and must meet demands for even higher breakdown voltage ability and large current interrupting ability. The performance of the vacuum interrupter is determined in large measure by contact materials in the vacuum container.
Desirable properties in a contact material for vacuum interrupters include a large interrupting capacity, high breakdown voltage, small contact resistance, small separating force of contact, low wearing out of control, small chopping current, good workability and mechanical strength, and the like. In using the conventional practical contact materials, it is actually difficult to satisfy all of the above-mentioned characteristics.
For instance, the copper(Cu)-tungsten(W) contact material shown in published unexamined patent application No. Sho. 55-78429 has very good interrupting ability, so that it is used mostly for purposes of load switch and contactor, or the like. However, copper has come limitations in its ability to interrupt large currents.
On the other hand, the copper(Cu)-chrome(Cr) alloy shown in published unexamined patent application No. Sho. 54-71375 has excellent interrupting ability, so that it is used more for interrupters, or the like, but it is inferior to the above-mentioned copper(Cu)-tungsten(W) contact material in breakdown voltage ability.
Besides the above mentioned contact materials for vacuum interrupters, some examples of contact materials used in the gas or oil industry are given in literature of "Funmatsu Yakin Gaku" (Powder Metallurgy) published by the Dally Industrial news, Tokyo Japan.
However, contact materials of silver(Ag)-molybdenum(Mo) alloy, of copper(Cu)-molybdenum(Mo) alloy, or the like disclosed in above-mentioned literature, are now rarely used for vacuum interrupters, because when they are used for contact for vacuum interrupters their breakdown voltage abilities are inferior to the above-mentioned copper(Cu)-tungsten(W) contact material, and their current interrupting abilities are inferior to said copper(Cu)-chrome(Cr) contact material.
As mentioned above, conventional contacts for vacuum interrupters have been used, making good use of their own characteristics; but, recently, demands for adaptations thereof to larger current and higher voltage have become more severe, and it has become difficult to satisfy these demands with the conventional contact material. Furthermore, for miniaturization of the vacuum interrupters, a contact material having even better characteristics is required.